Nadal needed nearly two and a half hours to get past the talented Czech 2-6, 6-4, 7-5, eight double faults doing little to help his cause in the second-round clash. Wimbledon champion Andy Murray, the fifth seed, fought back from a set down against another Czech, subduing Lukas Rosol 4-6, 6-3, 6-2.

The going was easier for four-time champion Roger Federer and fellow Swiss Stanislas Wawrinka, who is playing his first tournament since his Australian Open triumph. Federer, the former world number one who has fallen to eighth in the world and is seeded seventh here, defeated France’s Paul-Henri Mathieu 6-2, 7-6 (5).

“It was a difficult match to start against Ivo,” said Wawrinka, who didn’t face a break point and answered nine aces from Karlovic with eight aces of his own. “It’s never easy. He’s a tough player. “He doesn’t give you so much rhythm. But I’m really happy the way I was playing, the way I was aggressive on the court, and to win in straight sets was really important for me.”

Tricky situationNadal said Stepanek was a similarly tough opening opponent, his unpredictability making it hard to get in a groove.

“What you want to find in the first (match) is rhythm, and against him every point is different,” Nadal said.Nadal appeared to have gained control of the contest when he won the second set with a single service break and broke again to open the third.

He immediately gave the break back, however, and had to save three break points before holding in the sixth game. “It was a tricky situation in the 0-40,” said Nadal, who responded to the danger with a service winner, an ace and a backhand passing winner.

“After that, I think I played better,” said Nadal, adding that one benefit of the tough match was that it showed him the back trouble that hindered him in his Australian Open loss to Wawrinka — and which was still nagging him when he won in Rio last month — needn’t worry him. “Probably that match is going to help me understand that I really can start to serve normal again,” he said.